Aluminum containing small amounts of manganese constitute a class of known alloys having the corrosion resistance of aluminum with higher strength. The addition of manganese metal to molten aluminum to provide final alloys of this type is generally unsatisfactory because of the slow rate of dissolution thereof in the molten aluminum and poor manganese recoveries. As a result, to a considerable extent manganese has been added to molten aluminum, to provide the final alloy, in the form of a master aluminum-manganese alloy containing much higher (up to 30%) manganese contents. However, such alloys are costly and/or inconvenient to produce and handle.
A more recent method involves pre-mixing of finely divided normally alpha manganese containing particles with finely divided aluminum particles and compacting the mixture into a pellet or briquette. By reason of the presence of aluminum, which is commonly referred to as a "promoter material", the manganese dissolves more readily than the manganese metal, for when such a compacted mixture is added to a bath of molten aluminum the lower melting portion of the mixture, i.e. the aluminum, melts and thus assists in the dispersion of the remaining mass of manganese. The speed at which the manganese then dissolves in the molten aluminum is a function of its particle size, surface area, and bath conditions, such as temperature and amount of agitation. Nevertheless, at typical operating temperatures for aluminum baths in commercial operations, e.g. temperatures of about 1280.degree. F. to about 1500.degree. F., the solubility rate of such compacts is not as rapid as desired.
Because of the disadvantages of the current state of the art, it remains desirable to provide a manganese alloying additive and process for incorporating manganese into aluminum which will be capable of dissolving in the molten bath of aluminum in short periods of time with high recoveries of manganese in the final alloy.
It is a principal object of the present invention to provide a method for adding manganese to molten aluminum whereby the rate of solution of the manganese is markedly faster than heretofore.
It is another principal object of the present invention to provide a method for converting manganese into a physical form which enhances its rate of dissolution in molten aluminum.
A further principal object of this invention is to provide a mangangese alloying additive for addition to molten aluminum which has a fast rate of dissolution in the molten aluminum.
Still another principal object of the invention is to provide a novel method for producing manganese metal having a controlled particle size and a reduced fines content.
Other objects of the invention will become further apparent from the following specification and claims.